Catalyst for hydrocarbon steam cracking, method of preparing the same and method of preparing olefin by using the same

ABSTRACT

The present invention relates to a catalyst for hydrocarbon steam cracking, a method of preparing the same, and a method of preparing olefin by the hydrocarbon steam cracking by using the catalyst, and more specifically, to a catalyst for hydrocarbon steam cracking for preparing light olefin including an oxide catalyst (0.5≦j≦120, 1≦k≦50, A is transition metal, and x is a number corresponding to the atomic values of Cr, Zr, and A and values of j and k) represented by CrZr j A k O x , wherein the composite catalyst is a type that has an outer radius r 2  of 0.5R to 0.96R (where R is a radius of a cracking reaction tube), a thickness (t; r 2 −r 1 ) of 2 to 6 mm, and a length h of 0.5r 2  to 10r 2 , a method of preparing the same, and a method of preparing light olefins such as ethylene, propylene, etc., by performing the hydrocarbon steam cracking reaction in the presence of the composite catalyst. The present invention can provide catalysts for hydrocarbon steam cracking having high physical strength, excellent stability at high temperature, low non-activation due to coke, and improved yield and selectivity of light olefins.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/793,855filed Jun. 4, 2010, now U.S. Pat. No. 8,481,451 which matured out of theabove-identified application on Jul. 9, 2013, the present applicationwhich claims priorities from Korean Patent Application Nos.10-2009-0050333 and 10-2009-0076145 filed on Jun. 8, 2009 and Aug. 18,2009, respectively, in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a catalyst for hydrocarbon steamcracking for preparing light olefin, a method of preparing the same, anda method of preparing olefin by hydrocarbon steam cracking by using thecatalyst, and more specifically, to a catalyst for hydrocarbon steamcracking, which has excellent thermal stability at high temperature, lownon-activation due to coke, and improved yield and selectivity of lightolefin, a method of preparing the same, and a method of preparing lightolefin by using the catalyst.

BACKGROUND OF THE INVENTION

Ethylene and propylene, which are important raw materials ofpetrochemical products, are prepared by cracking hydrocarbon, which usesparaffin compound such as natural gas, naphtha, gas oil, etc., as maincomponents, at a high temperature of at least 800° C. in the presence ofa steam.

In the hydrocarbon steam cracking reaction, in order to increase theyield of ethylene and propylene, the conversion ratio of hydrocarbonshould be increased or the selectivity of olefin should be increased.However, since there is a limitation in increasing the conversion ratioof hydrocarbon or the selectivity of olefin only by the pure steamcracking reaction, various methods capable of increasing the yield ofolefin have been proposed.

In the hydrocarbon steam cracking reaction, there has been proposed thesteam cracking method using a catalyst as the method capable ofimproving the yield of ethylene and propylene. U.S. Pat. No. 3,644,557disclosed a method of using a catalyst made of magnesium oxide andzirconium oxide, U.S. Pat. No. 3,969,542 disclosed a method of using acatalyst including calcium aluminate as basic components, U.S. Pat. No.4,111,793 disclosed manganese oxide carried in zirconium oxide, EPLaid-Open Patent No. 0212320 disclosed an iron catalyst carried inmagnesium oxide, and U.S. Pat. No. 5,600,051 disclosed a catalyst madeof barium oxide, alumina, and silica. In addition, PCT Patent No.2004/105939 disclosed a method of using a catalyst made of potassiummagnesium phosphate, silica, and alumina. However, in the case of usingthese catalysts, the catalyst material functions as a thermal medium inthe carbon steam cracking reaction to improve the yield of olefin,however, is slight in the yield improvement of olefin as compared to thecase of using a non-active carrier.

Russia Patent No. 1,011,236 disclosed a potassium vanadate catalystformulated with boron oxide in an alumina carrier. However, in the caseof using alkali metal oxide or potassium vanadate catalyst, the yieldimprovement of olefin by the catalyst becomes small as well as the lossof olefin essentially occurs at high temperature for hydrocarbondecomposition. In other words, the catalyst can exist in a liquid phasein the inside of a high-temperature cracking reactor due to a lowmelting point of catalyst components and the catalyst components arevolatilized due to the fast flow of reaction gas to degrade the catalystactivation as the reaction time elapses.

U.S. Pat. No. 7,026,263 disclosed a method of using a hybrid catalystmade of molybdenum oxide, alumina, silica, silicalite, zirconium oxide,etc. Since the above-mentioned catalysts can be reacted at low reactiontemperature, but is operated at very low hydrocarbon flux, it isdifficult to directly apply the catalysts to the existing processes. Inaddition, the thermal stability of catalysts is significantly low at thereaction temperature of at least 700 to 800° C., such that the catalystactivation is lost.

In addition, since the existing cracking process is operated at highreaction temperature and high hydrocarbon linear velocity and generatesa large amount of coke, the generated coke should be combusted at hightemperature. In order to use the catalyst for a long time under thesevere operation conditions, the catalysts should be stabilized againstthe thermal/physical deformations. The foregoing related arts have aproblem in that the catalysts are vulnerable to the thermal/physicaldeformations or the stability thereof is not verified.

Therefore, in order to consider the economical efficiency of hydrocarbonsteam cracking process and avoid the complexity of process, a needexists for a catalyst that significantly improves the yield andselectivity of light olefin and has excellent thermal/mechanicalstability even at high temperature.

SUMMARY OF THE INVENTION

The present invention proposes to solve the above problem in the relatedart. The present invention provides a composite catalyst having aspecific type including active component represented byCrZr_(j)A_(k)O_(x) as a catalyst for hydrocarbon steam cracking, whichhas improved yield and selectivity of olefin, low non-activation due tocoke, and excellent thermal stability at high temperature, whenpreparing olefin by cracking hydrocarbon with a steam and a method ofpreparing the same.

In addition, the present invention to provide a method of filling acomposite catalyst for hydrocarbon steam cracking and a method ofpreparing light olefins by cracking hydrocarbon with a steam in thepresence of the filled composite catalyst.

The present invention is described in detail hereinafter.

In order to achieve the above aspects, there is provided a compositecatalyst for hydrocarbon steam cracking including an oxide catalyst(0.5≦j≦120, 1≦k≦50, A is transition metal, and x is a numbercorresponding to the atomic values of Cr, Zr, and A and values of j andk) represented by CrZr_(j)A_(k)O_(x), wherein the composite catalyst isa type that has an outer radius r₂ of 0.5R to 0.96R (where R is a radiusof a cracking reaction tube), a thickness (t; r₂−r₁) of 2 to 6 mm, and alength h of 0.5r₂ to 10r₂.

In addition, there is provided a method of preparing a compositecatalyst for hydrocarbon steam cracking including (a) mixing an oxidecatalyst (0.5≦j≦120, 1≦k≦50, A is transition metal, and x is a numbercorresponding to the atomic values of Cr, Zr, and A and values of j andk) represented by CrZr_(j)A_(k)O_(x) and a carrier; (b) molding amixture of the (a) in a specific type; and (c) sintering a molded objectof the (b) and preparing the sintered molded object in a ring type thathas an outer radius r₂ of 0.5R to 0.96R (where R is a radius of acracking reaction tube), a thickness (t; r₂−r₁) of 2 to 6 mm, and alength h of 0.5r₂ to 10r₂.

Further, there is provided a method of preparing light olefins includingcracking hydrocarbon with a steam in a reaction tube filled with thecomposite catalyst for hydrocarbon steam cracking according to thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a top view of a shape of a composite catalyst forhydrocarbon steam cracking in a ring type, which is filled in a reactiontube in a row and FIG. 1( b) is a front view of the composite catalystin a ring type.

FIG. 2 shows a composite catalyst used in Example 1 as one example ofthe composite catalyst for hydrocarbon steam cracking in a ring typewithout holes according to the present invention.

FIG. 3 shows a composite catalyst used in Example 2 as one example ofthe composite catalyst for hydrocarbon steam cracking in a ring typewith holes according to the present invention.

FIG. 4 shows a composite catalyst used in Example 3 as one example ofthe composite catalyst for hydrocarbon steam cracking in a ring typewith holes according to the present invention.

FIG. 5 shows a ration of methane/propylene according to reactiontemperature in the case where the composite catalyst according toExamples 1 to 3 is used as a catalyst in the hydrocarbon steam crackingreaction according to the present invention and in the case ofComparative Example 1 that does not use the catalyst.

FIG. 6 shows yield of ethylene and propylene that are products accordingto an operation time when the composite catalyst according to Example 3is used as a catalyst in the hydrocarbon steam cracking reactionaccording to the present invention.

DETAILED DESCRIPTION OF MAIN ELEMENTS

R: Radius of cracking reaction tube

r₁: Inner radius of ring

r₂: Outer radius of ring

r₂−r₁: Thickness of ring

h: Length of ring

DETAILED DESCRIPTION OF THE INVENTION

The advantages, features and aspects of the invention will becomeapparent from the following description of the embodiments withreference to the accompanying drawings, which is set forth hereinafter.

Hereinafter, the present invention will be described in detail.

When a composite catalyst that includes, as catalyst component, oxideincluding Cr and Zr and including one or more metal component selectedfrom a group consisting of Ti, Nb, Mo, V, Co, Ni, W, Fe, and P and ismolded in a specific type according to the present invention isprepared, the inventors confirmed that the composite catalyst hasexcellent catalyst activation to improve yield of light olefin, reducesnon-activation due to coke, is thermally/mechanically stabilized even athigh temperature not to cause deformations, thereby improving problemsof degradation of hydrocarbon decomposition activation and yield oflight olefin and completed the present invention based on this.

Composite Catalyst for Hydrocarbon Steam Cracking and a Method ofPreparing the Same

The composite catalyst for hydrocarbon steam cracking according to thepresent invention includes oxide defined by Formula 1 as catalystcomponent, wherein the composite catalyst has a type that has an outerradius r₂ of 0.5R to 0.96R (where R is a radius of a cracking reactiontube), a thickness (t; r₂−r₁) of 2 to 6 mm, and a length h of 0.5r₂ to10r₂.CrZr_(j)A_(k)O_(x)  Formula 1

In Formula 1, j is 0.5≦j≦120, preferably 5≦j≦90, and more preferably70≦j≦90, k is 1<k≦50, preferably 5≦k≦30, and more preferably 15≦j≦28,and x is a number corresponding to the atomic values of Cr, Zr, and Aand values of j and k.

In addition, A is one or more metal component selected from a groupconsisting of Ti, Nb, Mo, V, Co, Ni, W, Fe, and P.

FIG. 1( a) is a cross-sectional view of a cracking reaction tube filledwith a composite catalyst according to the present invention and FIG. 1(b) shows a composite catalyst without holes as the composite catalystaccording to the present invention.

When the composite catalyst is inserted into the cracking reaction tubehaving the radius R, it is preferable that a thickness t (that is,r₂−r₁) of the composite catalyst is in the range of 2 to 6 mm.Preferably, the outer radius r₂ has a value in the range of 0.5R to0.96R and more preferably, has a value in the range of 0.5R to 0.75R.Further, a length h preferably has a value in the range of 0.5r₂ to 10r₂and more preferably has a value in the range of 0.5r₂ to 5r₂.

When the thickness t (that is, r₂−r₁) of the composite catalyst is lessthan 2 mm, the composite catalyst can be crushed and when the thicknessis more than 6 mm, the differential pressure in the cracking reactiontube increases and the residence time of reaction products furtherreduces to reduce the yield of olefin.

When the outer radius r₂ of the composite catalyst is less than 0.5R,the composite catalysts are hard to fill in a row and when the outerradius r₂ is more than 0.96R, the composite catalyst is hard to insertand is crushed due to deformations.

Moreover, when the length h of the composite catalyst is less than 0.5r₂or more than 10r₂, gases inside and outside a heat exchanging medium arenot sufficiently mixed.

In addition, the composite catalyst according to the present inventionmay be a ring type with holes as shown in FIGS. 3 and 4 so that theinside/outside fluids can be exchanged and mixed.

When fillers in a ring type are filled in the cracking reaction tube ina row, a ‘channeling phenomenon’, which the fluids inside and outsidethe ring are unevenly heated and decomposed while channels areseparated, may occurs. This phenomenon cannot be solved since the mixingof fluids is insufficient only by open-cells existing in the fillers,but can be improved by forming holes so that the inside/outside fluidscan be exchanged and mixed at an outer wall of the ring.

The hole is a circle, wherein a diameter of the circle is preferably0.01r₂ to 2r₂. Preferably, at least two holes are formed at the outerwall of the ring in a length direction and a lateral direction,respectively. The diameter and number of holes may be changed. However,when there is a portion where the distance between the holes is reducedup to 3 mm, the strength of the ring is weak, such that the ring can beeasily crushed. Therefore, the number of holes is not limited, but ispreferably 2 to 50 and more preferably 2 to 10.

Moreover, since the differential pressure of the cracking reaction tubemay be increased due to the existence of the holes, an area occupied byall the holes regarding the composite catalyst is not more than 50%. Inorder to reduce the increase in the differential pressure inside thereaction tube due to the holes, the ring without holes and the ring withholes can be mixed and filled.

When the composite catalyst of the present invention is filled in thecracking reaction tube, the filling rate is not more than 50% and ispreferably in the range of 5 to 40%. When the filling rate is less than5%, the increase in the yield of olefin is insignificant and when thefilling rate is more than 40%, the residence time of the reaction gasreduces to degrade the yield of olefin.

The method of preparing compounds defined by Formula 1 includes: (a)preparing an aqueous solution by mixing water with Cr containingcompound and a Zr containing compound or a Cr—Zr containing compound;(b) preparing a slurry by adding ammonia liquor to the prepared aqueoussolution and co-precipitating them; (c) performing circulation heatingor hydrothermal treatment on the prepared slurry; and (d) preparing anoxide catalyst defined by Formula 1 by filtering, drying, and burningthe slurry.

The (a) includes preparing an aqueous solution by mixing water withmetal compounds.

The Cr containing compound and the Zr containing compound or the Cr—Zrcontaining compound may be used in salt types, such as sulfates,nitrates, oxalates, halides, chlorides, etc. Preferably, the nitratesare used.

In addition, the metal compounds, that is, the Cr containing compoundand the Zr containing compound or the Cr—Zr containing compound may befurther mixed with third metal compound. As the third metal compound,one or more compound selected from a group consisting of Ti, Nb, Mo, V,Co, Ni, W, Fe, and P. Preferably, Ti, Ni, and P are used and morepreferably, Ti and P are used.

The metal components of the third metal compounds may be used in types,such as salt, acid, oxide, hydroxide, alkoxide, etc. When the metalcomponent of the third metal compound is an alkoxide precursor type, thealkoxide is hydrolyzed in water and thus, can be precipitated as salt ina solid state, such that strong acid such as nitric acid may be added tothe alkoxide in order to dissolve the alkoxide.

The metal component of the third metal compound can be used by beingdissolved in water and then mixed with Cr and Zr aqueous solution or canbe used by being dissolved in water together with the Cr and Zrprecursors.

The aqueous solution, in which the above-mentioned components aredissolved, is heated and agitated and at the same time, may be agitatedfor at least one hour so that it is sufficiently mixed in the range thatthe temperature of the aqueous solution is 40 to 80° C., preferably 60to 70° C.

The (b) includes controlling pH to 7 to 9, preferably 8 to 8.5 by addingammonia to the aqueous solution of the (a) and co-precipitating them toprepare slurry.

The (c) includes calculatedly heating the slurry of the (b) for at least12 hours at the same temperature as the (a) or hydrothermally treatingit at an autoclave in the range of 60 to 150° C.

The (d) includes filtering, drying, and burning the circulation-heatedor hydrothermal-treated slurry of the step (c) to prepare a catalyst.

Preferably, the drying is performed for at least 2 hours at 120° C.Preferably, the burning is performed for at least 4 hours at 750 to1600° C. When the burning is performed in the temperature range, thesintering is not rapidly made, such that the catalyst activation is notlost.

In addition, the method of preparing a composite catalyst forhydrocarbon steam cracking includes: (a) mixing an oxide catalystcomponent defined by Formula 1 with a carrier; (b) molding the mixtureof the (a) in a specific type; and (c) sintering the molded object ofthe (b) to prepare the sintered molded object in a ring type that has anouter radius r₂ of 0.5R to 0.96R (where R is a radius of a crackingreaction tube), a thickness (t; r₂−r₁) of 2 to 6 mm, and a length h of0.5r₂ to 10r₂.

The (a) includes mixing the oxide catalyst component defined by Formula1 with the carrier.

Preferably, in the hydrocarbon steam cracking reaction, the catalystcomponent is mixed by 0.5 to 50 wt % based on the entire weight of thecomposite catalyst. When the catalyst component is mixed less than 0.5wt %, it is difficult to exhibit the performance as the catalyst andwhen the catalyst component is mixed more than 50 wt %, the strength ofthe catalyst is weak. At the mixing the catalyst component with thecarrier, a binder may be further mixed.

Examples of the carrier may include general carriers, such as alphaalumina, silica, silica-alumina, zirconium oxide, magnesium oxide,magnesium aluminate, calcium aluminate, silicon carbide, aluminumtitanate, zeolite, etc. Preferably, silicon carbide as a carrier isused. When the silicon carbide is used as a carrier, silicon and carbon,which are precursors of the silicon carbide, may be mixed with thecatalyst component. At this time, the sintering process of the (c) isperformed, such that silicon and carbon is converted into siliconcarbide.

The silicon carbide has a stabilized structure at high temperature of atleast 1000° C., has large thermal impact, carburization, and creepresistance, has low coke deposition, and has large thermal conductivity,such that it becomes a thermal transfer medium suitable for the crackingreaction. When the silicon carbide is used, the crushing due to impactcan be prevented and the amount of carbon deposit can be reduced.

The (b) includes performing a molding in order to make the mixture ofthe (a) in a specific type. In other words, the (b) includes performinga compression molding or an extrusion molding. Herein, as the moldingtype of the composite catalyst, several specific types may be used, butpreferably, a ring type is used.

In addition, holes may be formed at the outer wall of the compositecatalyst according to the present invention (FIGS. 3 and 4). The hole isa circle, wherein a diameter of the circle is preferably 0.01r₂ to 2r₂.Preferably, at least two holes are formed at the outer wall of the ringin a length direction and a lateral direction, respectively. The numberof holes is not limited, but is preferably 2 to 50 and more preferably 2to 10.

At this time, examples of methods for preparing the composite catalystfor hydrocarbon steam cracking having holes may include a method ofmaking the composite catalyst in a ring type, sintering them, and thenforming holes at an outer wall, a method of making a mold type in a ringtype with holes when performing the extrusion molding at the (b),injecting carrier catalyst component in the mold, pressing it to preparethe composite catalyst, and then sintering the composite catalyst, etc.,may be used, but are not limited thereto.

The (c) includes sintering molding having a specific type of the (b).The molding of the (b) is subjected to the sintering process, whichreduces the volume of the molding. Therefore, the molding is prepared asthe composite catalyst having desired size, density, and surface area.At this time, the composite catalyst according to the present inventionis prepared in a ring type that has an outer radius r₂ of 0.5R to 0.96R(where R is a radius of a cracking reaction tube), a thickness (t;r₂−r₁) of 2 to 6 mm, and a length h of 0.5r₂ to 10r₂.

When the outer radius of the composite catalyst is less than 0.5R, thecomposite catalysts are hard to fill in a row and when the outer radiusr₂ is more than 0.96R, the composite catalyst is hard to insert and iscrushed due to the deformations of the reaction tube at hightemperature. Moreover, when the thickness of the composite catalyst isless than 2 mm, the composite catalyst can be crushed and when thethickness is more than 6 mm, the differential pressure in the crackingreaction tube increases and the residence time of reaction productsfurther reduces to reduce the yield of olefin. Further, when the lengthof the composite catalyst is less than 0.5r₂, the composite catalystsare hard to fill in a row and when the length is more than 10r₂, thedifferential pressure is largely increased when the crushing isperformed.

Preferably, the sintering is performed for at least 2 hours, preferably6 to 24 hours at a temperature of at least 1200° C., preferably at atemperature of 800 to 2000° C.

As described above, the sintered composite catalyst is preferablyprepared to have a density of 0.5 to 3.5 g/cm³, up to 50 m²/g surfacearea, and compression strength of at least 1000 N.

Examples of the reactor applicable to the hydrocarbon steam crackingreaction may include a fixed bed reactor, a fluidized bed reactor, amoving bed reactor, etc. In particular, when the fixed bed reactor isused, the catalyst molded in a sphere type or a pellet type may be used,but has a problem in that the differential pressure is largely formed ina catalyst layer. To solve this problem, it is preferable that thecatalysts molded in specific types such as a ring type, a pipe type, atube type, etc., are filled in a row in order to maximally reduce thefilling rate of the catalyst layer.

At least one composite catalyst is inserted into the cracking reactiontube according to the length. In some cases, the composite catalyst isseparated into several ten to several hundred, which may be filled inthe reaction tube in a row.

In addition, the composite catalyst for hydrocarbon steam crackingaccording to the present invention may be prepared to having many hugepores.

At the (a) of the method of preparing a composite catalyst forhydrocarbon steam cracking, if organic polymer compound is mixedtogether when the oxide catalyst component defined by Formula 1 and thecarrier powder are mixed, many huge pores are generated inside thecomposite catalyst while the organic polymer material is decomposed atthe (c).

Preferably, examples of the organic polymer material may include highdensity polyethylene (HDPE), polymethylmethacrylate (PMMA),polyvinylalcohol (PVA), starch, etc. Preferably, the particle size ofthe polymer material is in the range of 2 to 600 μm and 1 to 20 parts byweight for every part by weight of the catalyst component and thecarrier powder is mixed.

Method of Preparing Olefin Using the Composite Catalyst

A method of preparing light olefins according to the present inventionincludes cracking hydrocarbon with a steam using the composite catalystfor hydrocarbon steam cracking according to the above mentioned method.

When the composite catalyst according to the present invention isapplied as a catalyst for hydrocarbon steam cracking, the reaction yieldcan be improved, the selectivity of light olefins, in particular,propylene can be improved, and the thermal stability can be increased.

The light olefin according to the present invention means olefin havingup to 4 carbon atoms and in particular, may include ethylene, propylene,etc.

The hydrocarbon steam cracking reaction for preparing the light olefinmay be performed under the conditions that reaction temperature is 600to 1000° C., a weight ratio of steam to hydrocarbon is 0.3 to 1.0, andspace velocity (LHSV) is 1 to 20 hr⁻¹.

In the reaction, examples of the applicable reactor may include a fixedbed reactor, a fluidized bed reactor, a moving bed reactor, etc. Inparticular, when the fixed bed is used, the catalyst molded in thesphere type or the pellet type may be used and has a problem in that thedifferential pressure is largely formed in a catalyst layer. Using thecomposite catalyst for hydrocarbon steam cracking according to thepresent invention can maximally increase the porosity of the catalystlayer, making it possible to solve the above problem.

The present invention will be described in detail with reference to thefollowing examples. However, these examples are illustrated by way ofexample only and the technical scope of the present invention is notlimited thereto.

EXAMPLES Example 1

A composite catalyst in a type as shown in FIG. 2 was prepared by mixingand sintering 10 wt % of CrZr_(83.3)Ti_(16.7)O_(x) and 90 wt % siliconcarbide and then filled in a reaction tube having a diameter of 4.3 cmand a length of 300 cm in a row. At this time, the filling rate is32.9%.

Example 2

A composite catalyst in a type as shown in FIG. 3 was prepared by mixingand sintering 10 wt % of CrZr_(83.3)Ti_(16.7)O_(x) and 90 wt % siliconcarbide and then filled in a reaction tube having a diameter of 4.3 cmand a length of 300 cm in a row. At this time, the filling rate is13.1%.

Example 3

A composite catalyst in a type as shown in FIG. 4 was prepared by mixingand sintering 5 wt % of CrZr_(83.3)Ti_(16.7)O_(x) and 95 wt % siliconcarbide and then filled in a reaction tube having a diameter of 4.3 cmand a length of 300 cm in a row. At this time, the filling rate is12.7%.

Comparative Example 1

Hydrocarbon steam cracking was performed in an empty reaction tubehaving a diameter of 4.3 cm and a length of 300 cm in which thecomposite catalyst was not filled.

Experimental Example

In the state where the composite catalyst of Examples 1 to 3 is filledor in the state where the composite catalyst is not filled (comparativeexample 1), ethylene and propylene were prepared in the followingmethods.

At this time, in the steam contact cracking reaction of hydrocarbon,naphtha was used as hydrocarbon and the composition and physicalproperties of the used naphtha are as follows.

TABLE 1 Physical Properties Initial Terminal boiling Boiling Composition(wt %) Density point Point n-paraf- 1-paraf- (g/cc) (° C.) (° C.) finfin Naphthene Aromatic 0.675 30.9 160.7 39.5 38.9 15.3 6.3

The naphtha and water, which are reactions, were injected into a reactorby a metering pump. At this time, the injection ratio of naphtha andwater became 2:1 based on weight ratio and the flux of naphtha wascontrolled so that LHSV is 10 hr⁻¹. The naphtha and water injected intothe reactor were mixed via each vaporizer, passed through a primarypreheater heated at 550° C., passed through a secondary preheater heatedat 650° C., and then injected into the reactor (300 cm in length and 4.3cm in diameter).

The contact cracking reaction occurred while the mixture of steamnaphtha via the secondary preheater passes through the reactor heated byan electric furnace. At this time, the electric furnace, which is a heatsource, was changed between 940 to 1060° C. and the outlet temperature(reaction temperature) was changed between 740 to 830° C.

Water and heavy oil were condensed and separated in a liquid phase whilethe reaction products passes through two condensers connected in seriesand the remaining gaseous mixtures were analyzed by a gas chromatographyconnected in on-line and then discharged.

After the above-mentioned naphtha contact decomposition process ismaintained for about 120 hours, coke was combusted and regenerated underan atmosphere of 800° C. steam-air.

The yield of ethylene was calculated by the following MathematicalFormula 1 and the yield of other products (propylene) was calculated inthe same manner.Yield of ethylene (wt %)=ethylene generation amount/naphtha injectionamount×100.  Mathematical Formula 1

TABLE 2 Heat Outlet source reaction Yield of products (wt %) Ratio ofTemperature temperature Ethylene + Ethylene to (° C.) (° C.) EthylenePropylene Propylene Propylene Comparative 980 766 22.69 16.57 39.26 1.37Example 1 1000 778 24.26 16.29 40.55 1.49 1020 787 25.89 16.16 42.051.60 1040 797 27.75 15.91 43.66 1.74 1060 812 29.31 14.48 43.79 2.02Example 1 940 763 19.79 15.89 35.68 1.25 960 777 22.03 16.02 38.05 1.38980 791 24.81 16.13 40.94 1.54 1000 804 26.6 15.78 42.38 1.69 1020 82129.51 14.62 44.13 2.02 Example 2 940 758 21.01 16.62 37.63 1.26 960 77523.29 17.13 40.42 1.36 980 789 25.47 17.22 42.69 1.48 1000 806 27.816.93 44.73 1.64 1020 824 29.51 15.83 45.34 1.86 Example 3 960 777 25.6717.35 43.02 1.48 980 792 27.74 17.06 44.8 1.63 1000 808 29.25 16.2845.53 1.80 1020 824 31.14 14.76 45.9 2.11

As can be appreciated from Table 2, when the composite catalyst in aring type having the outer radius of r₂=0.74R and not having holes isfilled (Example 1), the hydrocarbon decomposition activation wasincreased to increase the yield of ethylene as well as the ratio ofethylene to propylene was at the same heat source temperature ascompared to Comparative Example 1, but the selectivity of propylene wasthe same as Comparative Example 1 (FIG. 5).

When the composite catalyst according to Example 2 having the outerradius of r₂=0.6R and having four holes on the side surfaces thereof toreduce the filling rate is filled, the hydrocarbon decompositionactivation is further increased at the same heat source temperature toincrease the yield of ethylene and propylene as compared to Example 1.In addition, the selectivity of propylene was increased to largelyincrease the yield of propylene as compared to Example 1 (FIG. 5)Therefore, the ratio of ethylene to propylene was reduced as compared toExample 1.

Moreover, when the composite catalyst according to Example 3 having theouter radius of r₂=0.6R and having eight holes on the side surfacesthereof to reduce the filling rate is filled, the hydrocarbondecomposition activation as well as the selectivity of propylene isfurther increased as compared to Example 2. Example 3 reduces thenon-activation due to coke when being operated for a long time and isthermally/mechanically stabilized not to suddenly increase thedifferential pressure due to the crushing during the operation (FIG. 6)

As described above, the present invention provides the compositecatalyst for hydrocarbon steam cracking that has excellentthermal/mechanical stability at high temperature, low non-activation dueto coke, and improved yield and selectivity of light olefins.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A method of preparing light olefin comprising:cracking hydrocarbon with steam in a reaction tube filled with acomposite catalyst for hydrocarbon steam cracking prepared by mixing,molding and sintering of an oxide catalyst represented byCrZr_(j)A_(k)O_(x), wherein 0.5≦j≦120, 1≦k≦50, A is a transition metal,and x is a number corresponding to the atomic values of Cr, Zr, and Aand values of j and k, and a carrier, wherein the composite catalyst hasan outer radius r₂ of 0.5R to 0.96R (where R is a radius of a crackingreaction tube), a thickness (t; outer radius r₂−inner radius r₁) of 2 to6 mm, and a length (h) of 0.5r₂ to 10r₂.
 2. The method of preparinglight olefin of claim 1 comprising: wherein A one or more compoundselected from a group consisting of Ti, Nb, Mo, V, Co, Ni, W, Fe, and P.3. The method of preparing light olefin of claim 1 comprising: whereinthe composite catalyst has holes, the hole being a circle and a diameterof the circle being 0.01r₂ to 2r₂.
 4. The method of preparing lightolefin of claim 3 comprising: wherein an area occupied by the holes onthe side surface of the composite catalyst is up to 50%.
 5. The methodof preparing light olefin of claim 1 comprising: wherein a filling rateof the composite catalyst is up to 50%.
 6. The method of preparing lightolefin of claim 1 comprising: wherein the composite catalyst has adensity of 0.5 to 3.5 g/cm³, surface area of up to 50 m²/g, and acompression strength of at least 1000 N.
 7. The method of preparinglight olefin of claim 1, wherein the steam cracking is performed atreaction temperature of 600 to 1000° C., a weight ratio ofsteam/hydrocarbon of 0.3 to 1.0, and space velocity (LHSV) of 1 to 20hr⁻¹.